Im no expert, but know something of Rocks and Water quality as i live in Nebraska and we got horribly hard/alkaline water because of the Ogalla aquifer in the midwest, its pure limestone.
Im sure a google search on what kind of rock you have could tell you something about it...
All i know is that rocks make water more stable and harder, so its a good thing. If you have some vinager on hand, pour it on the rock. If it sizzles, its limestone and will make it harder.
It really depends on how hard and alkaline your water already is, and what your fish like. I know nothing about cichlids however. I know they dig around alot, and they do fine in the water up here and its very hard, so im gonna guess and say the rocks would be fine, especially since cichlids like to mess around in the substrate and bury stuff under rocks all the time. They'd probably love it.